iPhone static sounds

hello i just got an iPhone 3G from my friend, but there is something wrong with it. her mom only dropped it once, but ever since that the phone has been making a static type sound coming from the bottom speakers. it only happens when i hit the unlock button and when i try to play music. Please if anyone knows what i could do let me know. and sorry if there is another post out there like this one.

i have just talked to the person that i have got the phone off of, and she isn't really 100% sure when they got it. i only spent $40 for it. so i think i got a pretty good deal. but is there anything i can fix with it, or download something off cydia to fix it?